Laser beam projection apparatuses, such as, for example, point lasers, line lasers or in particular rotation lasers, are used in particular in construction or interior finishing, for example for vertically marking walls. A rotation laser marks a reference plane by means of its rotating laser beam. In this case, the laser beam itself can be emitted for example in a punctiform, linear or fan-shaped fashion. The laser light can be generated as continuous light or in a pulsed fashion. What is important here is that the laser beam is emitted with plane trueness, in particular horizontal trueness, that is to say that it remains exactly in the envisaged plane, in order to be able to preclude incorrect markings. In order to ensure this, conventional lasers of this type are generally equipped with a beam self-leveling functionality. In order to fulfill such a beam self-leveling functionality, various technical solutions are known, which can be of mechanical type and also optical type. By way of example, the laser core module can be suspended in pendulum fashion, such that a horizontal trueness can be produced with use of gravitation. The laser can also be equipped with an inclination sensor, in the simplest case a bubble sensor, for example, the display or signal of which can be read and used as initial variable for an active adjustment of the laser. A first adjustment of the horizontal trueness and calibration of the beam self-leveling functionality are typically carried out by the manufacturer prior to delivery of the laser.
The adjustment of the laser can change, however, as a result of various external influences, such as, for example, temperature and moisture fluctuations, mechanical shocks such as vibrations, etc. Therefore, at regular intervals or as required, it is necessary to test and recalibrate the plane trueness and/or horizontal trueness of the laser and the beam self-leveling functionality thereof and, if appropriate, to readjust the laser.
For fulfilling this task, laser beam horizontal trueness testing devices are known and described in the prior art. These known devices usually comprise, as basic components, a telescope and an inherent inclination compensator, which is intended to ensure that the optical axis of the telescope is always aligned horizontally. This is necessary, of course, in order that the testing device itself can be aligned perfectly horizontally, such that it can actually be used to monitor the horizontal trueness of another apparatus. In one known laser beam horizontal trueness testing device, which will be described in even greater detail below with reference to FIG. 1a, the telescope has an entrance objective having an image plane in which objects situated remotely, i.e. at infinite distance, are imaged. In the continuation direction of the optical axis of the objective, downstream of the image plane, an eyepiece is arranged for an observer, behind which eyepiece for testing the laser beam horizontal trueness of a laser beam projection apparatus, a planar image sensor, typically a camera, is arranged, onto which an incident laser beam is imaged. Usually, the center of the image sensor is arranged on the optical axis of the objective. In front of the objective, a diaphragm having a central light-transmissive opening is fitted on the optical axis of the objective, for example screwed onto the telescope. Such a commercially available testing device is equipped for example with an optical filter fitted in front of the objective, said optical filter being settable in two positions, whereby the intensity incident in the telescope can be reduced in two stages.
Such a commercially available testing device has a series of disadvantages. Firstly, the accuracy achievable therewith when testing the laser beam horizontal trueness of a laser beam projection apparatus is greatly restricted, as will be substantiated in greater detail below. Secondly, carrying out such testing is also complex. A first group of disadvantages is based on the imaging of the laser beam via an eyepiece. An eyepiece usually has only a small diameter and a short focal length, that is to say a great curvature of the lens surface. As a result, considerable optical distortions are inevitably produced over the extent of the field of view, the disturbance being least in the center of the eyepiece. Moreover, an eyepiece is typically arranged displaceably over a certain distance in the axial direction in order to enable an adaptation to the specific properties of an observer's eye. As a result, inevitably only an approximate, but hardly a highly accurate, positioning of the eyepiece is possible. What is particularly disadvantageous for a measurement result is an unintentional tilting of the eyepiece relative to the optical axis of the objective, said tilting occurring relatively easily. This produces an offset of an incident laser beam, which enters the telescope horizontally through the objective and should actually be imaged onto the point of intersection between the optical axis and the planar image sensor, on the image sensor, which then incorrectly indicates a deviation of the laser beam from the horizontal course, which deviation is not actually present at all. Axial movements or incorrect positionings of the eyepiece additionally impair the collimation of the laser beam on the image sensor. In addition, this device is considerably susceptible to vibrations, specifically to a greater extent, the further away from the image plane the image sensor is arranged. This device allows only basic, i.e. “yes-no”, checks as to whether a deviation from the horizontal course of the laser beam is present. Any kind of quantification of such a deviation, to say nothing of a more accurate analysis for determining the cause of such a deviation, is not possible with this device. Therefore, when a deviation of the emitted laser light of an examined laser beam projection apparatus from the horizontal is established, this known laser beam horizontal trueness testing device also cannot be used to provide assistance in readjusting the laser beam projection apparatus, rather the latter then typically nevertheless has to be sent in for service by the manufacturer.
Furthermore, such a testing device, in particular owing to the disturbance-susceptible positioning of the eyepiece that carries out imaging onto the image sensor, itself has to be regularly recalibrated and, if appropriate, readjusted, which necessitates service by the manufacturer in the case of such known devices.
In addition to the large number of disadvantages described with regard to the optical measurement accuracy that is achievable, said device for testing the laser beam horizontal trueness of a laser beam projection apparatus is moreover usable only with great effort for an operator. The diaphragm with its central opening that is fitted in front of the optical entrance of the telescope is absolutely necessary for this device in order to make it possible to distinguish a laser beam incidence which deviates from the envisaged horizontal and is to be corrected from a laser beam that actually arrives horizontally, that is to say runs parallel to the optical axis, but runs in a manner perpendicularly offset with respect thereto. This last in the case of said device would likewise lead to an offset of the point of impingement of the laser beam on the image sensor. In this case, it would actually even be advisable to make the dimensioning of the diaphragm opening as small as possible, in order to improve the distinguishability and thus the measurement accuracy of the apparatus. For the use of the apparatus, however, this means that a laser to be tested with regard to its laser beam horizontal trueness has to be aligned with the diaphragm opening very accurately in terms of its optical exit opening for the laser beam, i.e. has to be positioned at the level of the optical axis of the objective in the case of a desired horizontal laser beam path. This means stringent requirements made of a user for an accurate positioning of the laser beam projection apparatus to be tested. This described problem of mutual level setting and alignment is made even more difficult when testing invisible laser beams, for example infrared beams, since the visual monitoring by a user or the visible reference when the apparatus to be tested is set up in front of the telescope is absent in that case.
The known laser beam horizontal trueness testing devices thus not only have an inadequate optical measurement accuracy and only very limited usability and thus only little usefulness of the measurement results obtained with such a device, but also can only be operated with great effort by a user.